1. Technical Field
A capacitor, and more particularly, a method for forming the storage node of a capacitor are disclosed. The disclosed method simplifies the fabrication process, and improves the electrical characteristics of the semiconductor product by forming the storage node of the capacitor with no stepped portion between cell regions and peripheral circuit regions necessary for memory storage of semiconductor products of the next generation to which a fine line width is applied, and, at the same time, forming a guard ring for dividing the cell regions and the peripheral circuit regions.
2. Description of the Related Art
Generally, a capacitor is the part storing a charge and supplying the charge necessary for the operation of a semiconductor device. As a semiconductor device is being highly integrated, the size of unit cells is being decreased, and the capacitance needed for the operation of the device is being increased little by little. The capacitance needed by devices of more than 64M DRAM is currently over 30 fF per cell.
In a conventional process of forming the storage node of a capacitor, a polysilicon plug is formed by forming a contact for a storage node, depositing a polysilicon layer, and performing an etchback process. Then, a capacitor oxide film etching is performed by depositing a nitride layer as an etching barrier film, and depositing a PSG oxide film of a high wet etching speed, for thereby fabricating a capacitor of an inner or outer cylinder shape.
At this time, the etching barrier film acts as a dry etching barrier in the dry etching of the capacitor oxide film, and acts as a wet etching barrier in the wet etching of the capacitor oxide film. Thus, in case of increasing the size thereof, from the point of view of obtaining an etching selectivity, a cracking problem results due to a stress on a wafer.
If a thinner nitride film is used in order to avoid cracking, the nitride film gets attacked because of deficiency in a selection ratio in the dry etching of the capacitor oxide film, and even an inter-layer insulating film (ILD2) at lower portions is etched in the subsequent etching of the nitride film to thus become a leakage source, thereby causing the refresh characteristics of the capacitor to be degraded.
And, after etching the capacitor oxide film, a polysilicon layer, a storage node, is deposited, and then a capacitor dielectric film is deposited. Then, a PSG film or SOG film with a high wet etching speed is deposited on the front surface of the wafer, or a photoresist film is coated thereon, for thereby burying the inside of the structure of the inner cylinder.
Next, the polysilicon deposited in the cell and peripheral circuit regions is polished, and the PSG, the capacitor oxide film, is wet etched, for thereby forming a storage node module of the inner cylinder type.
However, in case of using this method, the capacitor oxide film in the peripheral circuit region as well as the capacitor oxide film in the memory cell region is removed in the wet etching process. Thus, a stepped portion as high as the storage node is generated between cells and peripheral circuits. In an exposure process, since there is no DOF (depth of Focus) margin, an inter-layer insulating film is formed, and then a chemical mechanical polishing process (CMP), is required. In order to enhance CMP uniformity, a cell recess masking process for partially etching only the insulating film in the cell region and etching processes are additionally required. Hence, the number of unit processes is increased, and the processes become complicated, for thereby increasing production costs.
A method for forming a storage node of a capacitor which simplifies the fabrication process, and improves the electrical characteristics of semiconductor products by forming the storage node of a capacitor with no stepped portion between cell regions and peripheral circuit regions necessary for memory storage of next generation semiconductor products to which a fine line width is applied, and, at the same time, forming a guard ring for dividing the cell regions and the peripheral circuit regions.
To achieve the above advantages a method for forming the storage node of a capacitor according to a first embodiment includes: forming a gate having a bit line and a spacer on a semiconductor substrate; depositing an inter-layer insulating film and a barrier nitride film on the resultant material; forming a contact hole by depositing a contact mask on the inter-layer insulating film and the barrier nitride film and etching films, and then forming a polysilicon plug by depositing doped polysilicon in the contact hole and planarizing the same by a polishing process; depositing a capacitor oxide film and a hard mask polysilicon film on the resultant material; forming an antireflection film on the hard mask polysilicon film to thereafter stacking a photoresist film thereon; forming a contact in cell regions and a guard ring for dividing cell regions and peripheral circuit regions by firstly etching the hard mask polysilicon film using the photoresist film as a mask and secondly etching the capacitor oxide film so that the polysilicon plug is exposed to the etched hard mask polysilicon film; forming a doped polysilicon layer and hemispherical grain protrusions in the contact and guard ring; stacking a buried layer on the resultant material to thereafter planarize the same by a CMP polishing process; stacking a photoresist film in the peripheral circuit regions in the resultant material to thereafter remove the buried layer buried in the polysilicon plug in the cell regions; and forming a storage node by removing the capacitor oxide film stacked in the cell regions and the buried layer in the grain protrusions by using the photoresist film as a mask.
The barrier nitride film is formed at a thickness ranging from about 200 to about 1500 xc3x85 by the LP-CVD method or the PE-CVD method.
When the barrier nitride film and the first and second inter-layer insulating films are dry etched, they are preferably over-etched to about 30% of the thickness thereof.
Upon forming a polysilicon plug in the contact hole, doped polysilicon having a phosphorus concentration of more than 4xc3x971020 atoms/sec is used by the LP-CVD method or the RTP method.
The capacitor oxide film is preferably formed by depositing a PE-TEOS film or a USG film at a thickness at which a capacitance of 25 fF/cell can be obtained.
The antireflection film is formed by stacking a non-organic or organic substance such as SiON at a thickness ranging from about 100 to about 1000 xc3x85.
Upon etching the capacitor film, the barrier nitride film at its lower portion is used as an etching barrier, and is over-etched to about 10 to about 100% of the thickness thereof.
The guard ring is formed to have a width ranging from about 0.1 to about 0.5 xcexcm, and the etching selectivity of the capacitor oxide film to the barrier nitride film ranges from about 5:1 to about 20:1.
The grain protrusions of the storage node are thermal doped or plasma doped under a phosphorus gaseous atmosphere.
The thickness of the storage node is formed less than about 1000 xc3x85 to prevent shorting in a cylindrical cylinder.
The buried layer is stacked at a thickness ranging from about 0.1 to about 0.5 xcexcm, and the photoresist film is stacked at a thickness ranging from about 0.1 to about 0.5 xcexcm.
Upon performing the CMP polishing process after stacking the buried layer inside the polysilicon grain, the storage node and the hard mask polysilicon film are CMP polished from about 1 to about 20% of the thickness thereof.
Upon removing the capacitor oxide film by etching, it is over-etched from about 50 to about 500% of the thickness thereof by using the barrier nitride film as an etching barrier film.
In addition, there is provided a method for forming the storage node of a capacitor according to a second embodiment which includes: forming a gate having a bit line and a spacer on a semiconductor substrate; stacking a polysilicon layer on the resultant material to thereafter form a polysilicon plug by the CMP polishing process; depositing an inter-layer insulating film and a barrier nitride film on the resultant material; depositing a capacitor oxide film and a hard mask polysilicon film on the resultant material; forming an antireflection film on the hard mask polysilicon film to thereafter stack a photoresist film thereon; and opening the polysilicon plug by firstly etching the hard mask polysilicon film using the photoresist film as a mask and then etching the barrier nitride film and the inter-layer insulating film.